Wooden aircraft and crash safety

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:

wren460

Member
Joined
Jun 20, 2022
Messages
24
Location
Arizona
Wrapping the wood longerons in the cabin/cockpit area doesn't sound like a bad idea. Maybe today we could use a synthetic fabric with good cut resistance and enough elasticity to let the wood frame flex some rather than fracture where the wrapping starts. Dyneema in a resin with a lot of "give"?
Innegra fabric, basically indestructible. Two layers on each side of a 1" foam core is nearly indestructible when hit real hard with a ball peen hammer. A six layer solid laminate, you can't break it in half.......Stuff is super light weight
 

Vigilant1

Well-Known Member
Supporting Member
Joined
Jan 24, 2011
Messages
7,901
Location
US
Innegra fabric, basically indestructible. Two layers on each side of a 1" foam core is nearly indestructible when hit real hard with a ball peen hammer. A six layer solid laminate, you can't break it in half.......Stuff is super light weight
How well does epoxy adhere to it? I understand that's an issue with Innegra and UHMWPE (aka Dyneema). Some of them are blended with fiberglass in the same cloth to improve adhesion.
 

wren460

Member
Joined
Jun 20, 2022
Messages
24
Location
Arizona
How well does epoxy adhere to it? I understand that's an issue with Innegra and UHMWPE (aka Dyneema). Some of them are blended with fiberglass in the same cloth to improve adhesion.
In my limited testing this does not seem to be an issue. Here is a link to the fiber manufacturer's web site Fibers — InnegraTech
Somewhere you can find a close up image of the actual fibers which have holes or voids in them to promote bonding. The destructive testing I've done did not show a propensity for delamination even a fairly thick multi layer laminate bent and folded over upon itself back and forth numerous times but doing so of course causes total destruction of the epoxy in that zone and perhaps some view this as delamination.
 

cluttonfred

Well-Known Member
Supporting Member
Joined
Feb 13, 2010
Messages
9,533
Location
World traveler
On a practical level, if you were to reinforce a wooden cockpit with some sort of resin and fabric to create a "crash cell" around the occupant, what would that entail? Here's the Evans VP-1 Volksplane, which is about as simple a wooden airframe as you are going to find. What would you have to do to create that crash cell. I suspect that it's a lot more work and a lot more additional weight than you might think at first glance.

1655982861070.png
 
  • Like
Reactions: BJC

TFF

Well-Known Member
Joined
Apr 28, 2010
Messages
17,353
Location
Memphis, TN
More money should be spent on components that prevent crashes like better engine parts and flight training than adding weight that would surely require you to use the safety enhancements.
 

Wanttaja

Well-Known Member
Joined
Sep 15, 2013
Messages
2,151
Location
Seattle, WA
On a practical level, if you were to reinforce a wooden cockpit with some sort of resin and fabric to create a "crash cell" around the occupant, what would that entail? Here's the Evans VP-1 Volksplane, which is about as simple a wooden airframe as you are going to find. What would you have to do to create that crash cell. I suspect that it's a lot more work and a lot more additional weight than you might think at first glance.
I think the gold standard for crashworthiness has to be a modern agricultural aircraft. And for that, you need a crash cage, not just a few reinforced longerons. You'll need a solid rollover structure fore and aft of the cockpit opening, as a minimum.

Found a curious bit in my 1998-2020 homebuilt accident database. It has almost the same number of Volksplane crashes as Fly Babies (16 VP vs. 17 'Babies). Yet only two of the VP accidents killed the pilot, vs. seven of the Fly Babies. That's a 12% fatality rate vs. 41%.

First thought that came to mind was the issues some have had getting the wing bracing right, but that was only two of the Fly Baby's fatalities. Other than that, no causes predominated. Of the two fatal VP accidents, one was stall/spin, and the other is probably chalked up to pilot inexperience (interesting case...see NYC99LA221).

For low-powered planes like VPs and Fly Babies, I tend to think the reduction in capabilities due to increased weight of pilot protection might result in a net loss in safety. *IF* there is a single low-hanging fruit, perhaps. An example might be good, solid roll-over structures both fore and aft of the cockpit.

Ron Wanttaja
 

BJC

Well-Known Member
Supporting Member
Joined
Oct 7, 2013
Messages
15,421
Location
97FL, Florida, USA
I think the gold standard for crashworthiness has to be a modern agricultural aircraft. And for that, you need a crash cage, not just a few reinforced longerons. You'll need a solid rollover structure fore and aft of the cockpit opening, as a minimum.
Yup, plus lots of HP to drag it up into the air.


BJC
 

Vigilant1

Well-Known Member
Supporting Member
Joined
Jan 24, 2011
Messages
7,901
Location
US
*IF* there is a single low-hanging fruit, perhaps. An example might be good, solid roll-over structures both fore and aft of the cockpit.
Re: Low hanging fruit for crashworthiness:
- Rollover protection (as you said)
- Very good occupant restraints (with well placed, strong anchors)
- Good crush space to reduce spinal compression (a seat pan with adequate stroke and/or a few inches Conform foam (or similar. Really similar).

Some folks might also argue for a helmet.

After that, the price and weight go up. Still might be worth doing more, but not until the first 3 are done.
 

wren460

Member
Joined
Jun 20, 2022
Messages
24
Location
Arizona
I think the gold standard for crashworthiness has to be a modern agricultural aircraft. And for that, you need a crash cage, not just a few reinforced longerons. You'll need a solid rollover structure fore and aft of the cockpit opening, as a minimum.

Found a curious bit in my 1998-2020 homebuilt accident database. It has almost the same number of Volksplane crashes as Fly Babies (16 VP vs. 17 'Babies). Yet only two of the VP accidents killed the pilot, vs. seven of the Fly Babies. That's a 12% fatality rate vs. 41%.

First thought that came to mind was the issues some have had getting the wing bracing right, but that was only two of the Fly Baby's fatalities. Other than that, no causes predominated. Of the two fatal VP accidents, one was stall/spin, and the other is probably chalked up to pilot inexperience (interesting case...see NYC99LA221).

For low-powered planes like VPs and Fly Babies, I tend to think the reduction in capabilities due to increased weight of pilot protection might result in a net loss in safety. *IF* there is a single low-hanging fruit, perhaps. An example might be good, solid roll-over structures both fore and aft of the cockpit.

Ron Wanttaja
Great discussion here about crash worthiness. Personally, I've been working on a VP-2 design modification wherein I plan to use modern composite materials in conjunction with natures natural composites (wood). The earlier information regarding the twisting of the fuselage in response to aileron input could be solved with the use of Divinycell foam core sandwich panels along the fuselage bottom, rear bulkhead behind the seat and even the cockpit fuselage sides while at the same time enhancing crash worthiness. While carbon fiber tends to shatter when overloaded, one could do a hybrid layup of carbon and Innegra or Kevlar. Incredible torsional stiffness can be had with sandwich cores and carbon fiber set at 45 degrees on both surfaces. This results in a panel wherein the panel itself provides the torsional resistance and not just the fuselage box structure as with the use of thin plywood skins.

Considering the high cost of quality wood these days ( Has anybody priced spar sized spruce lately?), it makes a lot of sense to reinforce a wooden structure using composites. Some structural elements could be entirely replaced with composites. Of course the entire structure could be composite but in keeping with simplicity and to avoid expensive tooling, a combination of wood elements with composites makes some sense.
 

radfordc

Well-Known Member
Joined
Feb 5, 2008
Messages
1,546
Re: Low hanging fruit for crashworthiness:
- Rollover protection (as you said)
- Very good occupant restraints (with well placed, strong anchors)
- Good crush space to reduce spinal compression (a seat pan with adequate stroke and/or a few inches Conform foam (or similar. Really similar).

One reason I quit flying my Eindecker is the lack of roll over protection. In an off field landing it would likely end up upside down and visions of Charlie Hilliard run through my mine.

A friend had a remarkable crash in his Eindecker. At an altitude of over 100 ft AGL he lost an engine....as in it fell off the front of the plane! (Loose exhaust pipe into the prop, massive vibration, you know the rest). He had a video camera running and it happened so fast you couldn't tell what happened. The plane pretty much fell out of the sky in a wings level attitude. The gear collapsed, the seat structure collapsed, and he survived in better condition than you would expect. One piece of aluminum tube did pierce the seat pan but just missed him.
 

PiperCruisin

Well-Known Member
Supporting Member
Joined
Jan 17, 2017
Messages
452
Location
Idaho
Yup, plus lots of HP to drag it up into the air.


BJC

We have some crop dusters and SEATs at our airport. I thought the SEATs would fly great with the big wings and turboprop. Nope. They climb out at 200-300 fpm. On hot summer days, when they tend to fly, it makes me a little queasy to watch (feel like I'm waiting for a train wreck). The crop dusters do a little better. Stopped complaining about my 600 fpm climb.
 

PiperCruisin

Well-Known Member
Supporting Member
Joined
Jan 17, 2017
Messages
452
Location
Idaho
Sorry, but I assume you are not talking about flying Spanish cars…SEATs?

Looks like that flies better. No, I was talking about Single Engine Air Tankers.

Back on topic, I think the steel truss structure provides the best protection, but there are limits. Not sure I understand the huge interest in crashworthiness. Time is better spent discussing crash avoidance.
1656020351051.png
 
Top